Your RV holding tank can be a source of foul odors if you do not tend to it properly. The most obvious way to eliminate RV holding tank odors is to dump and clean your holding tank as often as recommended by the manufacturer's instructions. Use an RV holding tank cleaning kit to clean the tank completely. Another way to reduce the odor is to request that solid waste be disposed of in a plastic bag that is immediately removed from the RV. There are RV holding tank treatment kits that can help reduce odors, but they must be used only as per the manufacturer's instructions.